Temp Defense by Viola Grace

Haley is a temp on a short-term contract. It turns into an experiment and a fight for the survival of her world.

Haley is in her second week of a file-sort contract. She’s cleared to work with military records and has been slogging through years of research on artifacts that are only referred to vaguely. She is looking through a file and finds a piece of jewellery in the file with a lot of notes. She grabs the file and the bracelet and slips down the servants’ stairs to hand them off to the researchers in the basement, and that is where things go wrong.
The world is in danger. A rift of temporally stuck, highly radioactive marauders manage to saw through the space between worlds every six centuries. They are due any day now, and the military and family responsible for the defense are struggling to find the means to unlock the weapons they need. The original defenders never leave any clues, just the vague weapons.

Haley’s attempt to sneak the file into the lab is thwarted when a test subject is turned to ash. She’s caught, and she’s next.